Pharmacodynamics, Drug Interactions, and Adverse Drug Reactions

Comprehensive vocabulary flashcards covering Chapter 8: Pharmacodynamics, drug interactions, agonist and antagonist categories, drug tolerance, addiction, adverse reactions, and FDA pregnancy safety categories.

Pharmacodynamics

The term used to describe the way a drug interacts with the body, specifically target receptors, membranes, cells, tissues, organs, or the whole body.

Onset of Action

The time that elapses from the administration of a drug until its therapeutic effect is first noted.

Peak Effect

The time that elapses when a drug reaches its highest level of therapeutic effectiveness.

Duration of Action

The total time that elapses from the onset of drug action to the termination of action, which ceases through the pharmacokinetic processes of metabolism and excretion.

Drug Receptor Interactions

A mechanism of drug action where a drug molecule binds to protein or glycoprotein receptors on the plasmalemma, an organelle, or within the cytoplasm following a lock-and-key model; no reaction occurs if the molecule does not fit, a partial reaction occurs with a partial fit, and a full reaction occurs with an exact fit.

Drug Enzyme Interactions

A mechanism of drug action occurring when a drug speeds or inhibits the catalytic activity of an enzyme or alters the response of cells affected by that enzyme.

Nonspecific Responses

Drug actions that do not rely on drug receptor or enzyme interactions, but instead function by congregating on the plasmalemma or infiltrating it to act directly on cellular contents.

Chemical Interactions (Pharmacology)

Drug effects that occur without altering cellular function, such as sodium bicarbonate ($NaHCO_3$, pH $8.4$) neutralizing stomach hydrochloric acid ($HCl$, pH approximately $1.5$) to produce salt ($NaCl$), carbon dioxide ($CO_2$), and water ($H_2O$).

Synergist

A drug that works together with one or more other drugs to produce an enhanced effect, making the cumulative effect of the combined drugs greater than the effect of each drug individually (e.g., acetaminophen combined with codeine to form Tylenol #3).

Agonist

A drug that stimulates or prolongs the action of another drug or naturally occurring body substance, though it may not produce an action of its own (e.g., hyaluronidase [Amphadase®] added to lidocaine hydrochloride [Xylocaine®]).

Strong Agonist

An agonist that produces the greatest possible therapeutic effect even when occupying only a small percentage of available cell receptors.

Weak Agonist

An agonist that produces approximately the same therapeutic effect as a strong agonist, but must occupy a much higher percentage of target cell receptors to do so.

Partial Agonist

An agonist that produces only a weak therapeutic effect even when all available cellular receptors are fully occupied.

Antagonist

A drug that prevents or reverses the effect of another drug or naturally occurring body substance without producing an effect of its own (e.g., naloxone hydrochloride [Narcan®] reversing narcotic sedation, hypotension, and respiratory depression).

Competitive Antagonism

A surmountable form of antagonism occurring when the antagonist competes for and binds to the receptor normally occupied by the agonist (initial drug), which can be overcome by administering higher doses of the initial drug.

Noncompetitive Antagonism

An insurmountable form of antagonism occurring when an antagonist binds to an alternate receptor site, inducing a conformational change that renders the initial drug's receptor site unrecognizable and unusable.

Irreversible Antagonism

An insurmountable form of antagonism (also known as nonequilibrium competitive antagonism) where the antagonist binds permanently to the receptor site.

Physiological Antagonism

A form of antagonism occurring when two concurrently administered drugs produce opposing effects that effectively cancel each other out.

Antagonism by Neutralization

A form of antagonism occurring when two drugs bind directly to each other, inactivating both substances.

Additive

A substance combined with an initial drug to produce synergistic or agonistic effects, dilute, reconstitute, activate, preserve, flavor, or alter the pH of the formulation.

Excipient

A pharmacologically inactive additive that does not alter the performance or function of the active drug, such as hydrochloric acid ($HCl$) added as a buffer to lower the pH of naloxone (Narcan®).

Indications

The clinical reasons why a drug is prescribed, determined by the patient's medical condition, circumstances, and the established therapeutic effects of the drug.

Contraindications

The clinical reasons why a drug should be avoided, based on patient factors such as age, size, pregnancy, or comorbid organ dysfunction.

Side Effects

Expected, undesirable, generally mild, and manageable non-therapeutic effects of a drug, such as dry mouth, nausea, constipation, or drowsiness.

Secondary Effects

Known, predictable side effects of a drug that prompt its clinical application for alternative therapeutic purposes (e.g., using diphenhydramine hydrochloride [Benadryl®] as a sedative).

Adverse Effects

Serious, harmful, and undesirable drug effects that may be predictable or unexpected, including severe allergic reactions, alopecia, bone marrow depression, or vital organ damage such as liver damage.

Toxic Effects

Poisonous drug manifestations capable of causing injury or death, typically resulting from drug overdoses or severely impaired drug metabolism or excretion.

Teratogenic Effects

Drug-induced adverse effects that disrupt embryonic or fetal development, resulting in structural congenital defects present at birth.

FDA Category A

The FDA pregnancy safety category indicating that adequate, well-controlled human studies have demonstrated no risk to the embryo or fetus during any trimester.

FDA Category B

The FDA pregnancy safety category where controlled human studies show no risk despite animal findings, or where animal studies show no risk and human studies are lacking; carries slight risk.

FDA Category C

The FDA pregnancy safety category where animal reproduction studies show adverse fetal effects (or are lacking) and adequate human studies are missing, but potential benefits may warrant use despite risks.

FDA Category D

The FDA pregnancy safety category with positive evidence of human fetal risk, but potential therapeutic benefits may outweigh risks in life-threatening situations or serious diseases.

FDA Category X

The FDA pregnancy safety category where controlled human and animal studies demonstrate fetal abnormalities, rendering the drug strictly contraindicated during pregnancy because risks clearly outweigh any possible benefit.

Iatrogenic Response

A complication inadvertently induced in a patient by a healthcare provider or resulting from medical treatments or diagnostic procedures (e.g., nosocomial infections or pharmacologic adverse effects).

Drug Tolerance

A state of decreased responsiveness to a drug over time that requires progressively higher dosages to produce the intended therapeutic response.

Metabolic Tolerance

A type of drug tolerance (also known as dispositional tolerance) characterized by accelerated drug metabolism within the body.

Cellular Tolerance

A type of drug tolerance (also known as downregulation or reduced responsiveness) in which the total number of target cell receptors available to bind the drug decreases.

Behavioral Tolerance

A form of drug tolerance wherein an individual intentionally learns behavioral adaptations to conceal the observable effects of the drug.

Addiction

A physical or psychological state of dependence where a drug is required for an individual to function in a seemingly normal manner.

Withdrawal

The physical and psychological manifestations (also known as detoxification) that emerge when a dependent individual abruptly or gradually discontinues drug use.

Rebound Effect

A withdrawal phenomenon wherein the specific clinical condition or symptom for which a drug was originally prescribed returns with greater severity until physiological homeostasis is reestablished.